Power semiconductor devices are used in power applications to switch external loads. The power semiconductor devices either can be discrete components or can be integrated into smart power integrated circuits (“ICs”). During operation, the power semiconductor devices should be protected from high temperatures and high temperature gradients to ensure product reliability. Single-pulse failures are typically caused by the highest temperature in the power semiconductor device. Failures under cyclic loading typically occur in the metallization or in the bond wire connections. For automotive 12 V-systems, product reliability under repetitive high-current operation is particularly important for market acceptance.
To reduce or prevent temperature-induced failures, a local temperature is sensed in a power semiconductor device, and the operation of the device may be altered or stopped if the sensed temperature exceeds a temperature limit. Temperature measurements in semiconductor integrated circuits can be based on reverse- or forward-biased characteristics of a p-n junction, which is generally used for temperature sensing in most semiconductor power devices.
Alternatively, or in addition to, an absolute temperature measurement, a spatial temperature difference can be measured across the semiconductor chip. Such a temperature difference can, for example, be measured with two p-n junctions. Alternatively, a Seebeck temperature difference sensor can be used.
The Seebeck effect, employed in Seebeck temperature difference sensors, produces an electric field in every material in the presence of a spatial temperature gradient, and may be used to sense a temperature difference. The magnitude of the Seebeck effect varies among materials. The magnitude of the Seebeck effect is characterized by the Seebeck coefficient alpha (“α”). The Seebeck coefficient alpha is particularly large in semiconductors and particularly small in metals. A Seebeck temperature difference sensor typically includes two traces of materials that differ in their Seebeck coefficients. These two traces are electrically connected to each other only in the hot region. This electrical connection is ideally a low ohmic junction without nonlinearities. In the cold region, the two traces are electrically isolated from each other and are connected to sensor circuitry. In the presence of a temperature difference, a voltage develops along each trace due to the Seebeck effect. Because the Seebeck coefficients are different in the two materials, the voltages across the two materials are different from each other. Hence, the sum of the two voltages does not vanish, and the sum is proportional to the temperature difference. In the cold region, the sum of these two voltages is measured by the sensor circuitry. In contrast to p-n junctions, the Seebeck voltage develops along the trace of the materials, and not at the junction of the two materials. The voltage only depends on the temperature difference; it is not dependent on the routing of the traces.
Compared to p-n junctions, Seebeck temperature difference sensors may be constructed with smaller size and simpler driving circuitry. Because the output voltage of a Seebeck temperature sensor is proportional to a temperature difference, no current sources are needed as in the case of p-n junction temperature sensors.
Integrated temperature sensors have become an essential part of a device protection strategy, particularly for a power semiconductor device. However, such integrated temperature sensors should work reliably in an electrically noisy environment because a large time rate of change of voltage (“dV/dt”) and a large time rate of change of current (“dI/dt”) can occur during switching of a power semiconductor device. Power semiconductor devices used in electrically noisy environments can compromise a small signal level produced by a temperature-sensing device based on the Seebeck effect.
Thus, there is a need for a process and related method to provide a signal representing a temperature difference, which may include an added absolute temperature, in an integrated circuit that provide a reliable representation of temperature, and that may be required to operate in an electrically noisy environment, overcoming deficiencies of conventional approaches.